It is well-known to provide an autonomous carrier, such as a carrier for performing a conditioning operation on the surface over which it traverses, with sensing and guidance and control systems that allow the carrier to orient itself on the surface and carry out its functions while avoiding obstacles or obstructions. Such systems are commonly used with robot vacuum cleaners. Examples of these systems are disclosed in U.S. Pat. No. 5,935,179, WO9526512 and Patent Abstracts of Japan, abstract of JP 9-319435. However, obstacles will not be avoided in all instances and it is desirable that the carrier possesses an obstacle-sensing capability such that the carrier will free itself when it comes into physical contact with, or bumps into, an obstacle or obstruction. It is further desirable that the obstacle-sensing capability be sensitive to even slight contacts between the carrier and an obstacle, and not depend on a forceful engagement of the two.